The present invention relates generally to large diameter seals, and methods of making them, and more particularly, to such seals which contain a solid polytetrafluoroethylene (PTFE) or like fluorocarbon lip. Whereas seals having a PTFE material or the like for a lip have a number of advantages, including excellent abrasion resistance and excellent chemical and other solvent resistance, such seals have been relatively difficult and expensive to manufacture in large diameters.
Such large diameter seals are used, for example, to seal the lubricant into the bearings of huge rollers, such as the rollers used in steel mills, and of the same time, exclude contaminants from the rollers. Such rollers commonly have a diameter of from 24 inches to 48 or even 60 inches, or perhaps more.
Comparatively recently, there have been in use modern windmills with enormous blades turning turbines to generate electricity. These windmills customarily have very large shafts, perhaps two feet or more in diameter. These shafts need seals having the advantages of tetrafluoroethylene lips, particularly the excluder function, in view of the conditions under which these seals operate.
However, the use of such seals has been somewhat limited because of the expense of making such seals. At any rate, a more economical but still highly effective seal is needed and would be greatly desired.
The difficulty in manufacturing seals of this large diameter type are that, considering first the raw materials from which the lips are made, there have been at least two methods, each one of which has substantial drawbacks. One method of making such seals is to cut off a thin end of a cylindrical billet of PTFE, so that a huge diameter but thin ring of a PTFE material is formed. However, it is extremely expensive to obtain a billet of the size needed to accomplish this task.
The method of forming the lip portion of a seal from sheet material is not a problem with seals of a small diameter. However, when it comes to large diameters, such sheets of the proper size are prohibitively expensive, if indeed they can be found. Moreover, the enter center section, which would then be cut out, is normally wasted. In some cases, the remaining sheet must await formation of a smaller diameter seal. There may not be a demand for the intermediate sizes that could use the large remaining sheet of material.
However, with the present invention, it is possible to use very commonly available strips of material, which may then be flanged and formed with a slightly larger outside diameter than inside diameter and finally into a large closed loop of material. The inside diameter (“i.d.”) of such a loop may then be used as the primary lip of such large diameter seal.
The material from which the lip is made is readily available as a very long strip at reasonable cost. Such strip material may typically have a length of up to several hundred feet, a width of 1 to 1.5 inches, and a thickness of 0.015 to 0.060 inches, usually, 0.030 to 0.050 inches. According to the invention, material in this form may be flanged so as to form two angularly related legs, typically 30° to 45° apart. Thereafter, the strip may be notched at intervals of 1 or 2 inches, or have holes punched in it together with a series of slits to the outer diameter (“o.d.”). Such cuts enable the (PTFE) material to be curved so it can be formed into a continuous circular loop. This is done by placing the contoured ends of the strip of material in abutting relation and overlaid with a supplemental piece of a thin fluorocarbon (PTFE) tape. For such purposes, the tape may be a 0.007″ in thickness, for example, and placed over both ends, which are then raised to a temperature in the vicinity of 500°–550° F. or even greater.
Having thus been formed and notched or slit on the outside diameter, such a lip is thereafter placed between an inner and outer case and, with the help of gasketing means such as a formed rubber gasket, compressed into position between two L-shaped flanges, the outer one of which is crimped over the inner one to keep the inner casing in place.
An alternate method involves a slightly different form of notching the exterior by forming holes and slits therein. In addition, there is a method which does not involve actually piercing through the outer diameter of the seal material, but which is formed by placing V-shaped debossments or depressed areas of significant depth in the outside diameter of the lip material. This makes the lip portion susceptible to being curved on the outer diameter and is also useful in this connection.
Accordingly, in view of the failure of the prior art to provide large diameter, PTFE or like lip seals, it is an object of the invention to provide an improved large diameter seal having a lip formed from a PTFE or like material.
Another object is to provide a novel method or methods of making such seal.
Another object is to form such a seal by steps which include selecting a readily available PTFE material in the form of a thin, narrow strip, joining the ends, flanging the strip thus formed and imparting an increased outside diameter to the strip.
Another object of the invention is to provide one or more methods of forming the raw material such as PTFE strip into a gradually curving outside diameter suitable for making into an effective seal.
A still further object of the invention is to provide a system using a roller, preferably heated, and a puncturing or cutting device which will flange the material and notch the outside diameter of a strip of material so as to render it suitable for seal manufacture by a novel method.
A further object of the invention is to provide a seal which is flanged and contains a large number of radial notches so as to effectively enlarge the outer diameter of the seal into which it is made.
Another object is to form the lip material into a moderate or shallow V-shape flange so that the inside diameter of the flange thus created is not overly strained during manufacture.
A further object of the invention is to provide a method of notching the outside diameter of seal raw material in order to allow it to be shaped into an enlarged dimension in relation to the inside diameter of the lip.
The objects and advantages of the invention are achieved by flanging an elongated strip of PTFE or like material, allowing the opposite edge of the strip from the flange to be elongated or thinned, placing the thinned or cut edge and an adhesive between inner and outer cases, and crimping the outer case over the inner case to hold the lip in place so as to form a large diameter PTFE or like seal.
The manner in which these and other objects and advantages of the invention are achieved in practice will be more clearly understood when taken in connection with the following description of the preferred embodiments of the invention and shown in the drawings in which like reference numbers indicate corresponding parts throughout.